From: Guy Atkins (gatkins@gatkins.seanet.com)
Date: August, 1995
Original source: Usenet's rec.radio.amateur.antenna

Wouldn't the mismatch affect the aerials directional characteristics, and (even worse) allow the coax cable to pick-up signal on its outer shield, thus negating the reason we are using the coax (to remove local QRM and local stations on adjacent frequencies)?

I tend to agree with you about the directional loss... not so much from theoretical knowledge but from having DXed with Beverages for 4-5 years with a direct Bev-coax connection, and then for the last 5 years with a impedance matching device in between.
I believe that the directionality when using a 10:1 matching transformer (per design shown in Fine Tuning's Proceedings) has been better on MW and tropical bands during my DXpeditions. I have not done a direct, "A-B" comparison, but it is my judgement based on 20-25 Beverage expeditions since I started using the matching transformers. I have five identical "Bev Matchers" that I use on DXpeditions.
I also like the fact that a matching transformer ensures, within reason, the best possible signal transfer. There *are* occasions when geomagnetic conditions, T-storm static, etc. are EXTREMELY quiet and favorable; when I seek out very weak transpacific MW DX I don't want ANY signal loss in my antenna system if I can help it! Noted MW DXer Patrick Martin in Oregon, USA, feels the same way as I do about this. Those who say that "because we don't transmit on our antennas means that we can tolerate all sorts of mis-match" must never spend their time crawling around on the noise floor of their receivers. Sometimes the real DX is WAYYYY down in the mud! I know that a 3db loss or gain of signal strength is barely discernable, but a Beverage antenna is not particularly efficient and we can use all the signal our antennas can generate.
However, we must keep in mind that actual impedance of the Beverage antenna varies with frequency, wire height and size, rainy weather, and so on. The 10:1 transformation offers a good starting point for bringing the antenna's impedance closer to a nominal 50 ohms.

From: Steve Whitt
Date: August, 1995
Original source: Usenet's rec.radio.amateur.antenna

Guy Atkins wrote:
Those who say that "because we don't transmit on our antennas means that we can tolerate all sorts of mis-match" must never spend their time crawling around on the noise floor of their receivers. Sometimes the real DX is wayyyy down in the mud! I know that a 3db loss or gain of signal strength is barely discernable, but a Beverage antenna is not particularly efficient and we can use all the signal our antennas can generate.

This is absolutely true. I have, to my surprise, found several times on DX-pedition in Scotland the AM band to be so quiet that I have chased signals into my receiver noise floor! This happens in the hours after local sunrise with the antenna pointing west into the receding darkness. Many is the time I have heard US, Canadian and Alaskan AMers between 1 and 3 hours after sunrise. On two glorious occasions Alaska refused to fade out completely and was still there at local midday in October.
On such DX-peditions we use a splitter to share signal from the aerial to two or three receivers and when signals get weak this almost leads to punch-ups in the shack over who can have the the last microvolt!! So, as you can see, signal loss at a mis-match or on a long feed line can be an issue. All the seasoned DXers I know take a low noise preamp to use in front of what are already sensitive receivers.
However I have yet to notice this phenomenon at home in Southern England as there is just too much man-made interference & noise around.